1. Field of the Invention
The invention is generally related to the fields of biocides and biocidal and/or sporicidal coatings.
2. Description of the Related Art
Decontamination and neutralization of surfaces from bacteria and spores is a complex process that involves multiple technologies and various approaches, depending on the nature and extent of contamination. There are a variety of commercially available biocides and antiviral coatings; however, there are very few that claim to be effective as sporicides. Moreover, many decontaminating agents and solvents used to prepare them must be mixed onsite and applied for effective use.
The ability to decontaminate chemically-resistant, coated painted surfaces inoculated with anthrax spores is extremely important. The anthrax spore is the most persistent of all biowarfare agents. To kill them, the most potent biocides/sporicides must be employed. Irradiation is frequently necessary and often ineffective due to the robustness of dormant or weaponized spores. Such spores may remain dormant for decades, yet are easily converted into the harmful or lethal vegetative form within minutes under ideal conditions.
Most conventional liquid sporicidal agents fall into three broad categories: halide releasing compounds (e.g., hypochlorites and iodophores), reactive oxygen releasing agents (e.g., peroxides and peracetic acid), and aldehydes (e.g., formalin and glutaraldehyde) (Russell, Clin. Microbiology Rev. 1990, 3, 99. All referenced publications and patent documents are incorporated herein by reference). Activity of all of these agents depend on destruction of fundamental metabolic processes and organic structures, thus making them extremely hazardous to personnel in many cases (Cross et al., Appl. Environ. Microbiol. 2003 69, 2245). Furthermore, many of these agents rely on the generation of very reactive chemical species and are thereby inherently unstable. Most commercial sterilants require activation prior to use and subsequently lose effectiveness within hours. The efficacy of some agents such as hypochlorites is rapidly attenuated by the presence of organic matter. Aldehydes are effective sporicides only at relatively high concentrations as liquids and require high relative humidity for effectiveness as vapors. Decontamination frequently utilizes extremely toxic gases such as ethylene oxide, chlorine dioxide, and methylene bromide (Whitney et al., Emerging Infectious Diseases 2003, 9, 623). Sporicidal efficacy of these gasses requires high relative humidity, and their use requires very careful attention to personnel safety. Anthrax spores pose a particularly difficult problem with respect to monitoring the success of the decontamination efforts. Previous literature reports that a variety of other functional groups have been effectively used as biocides; however, none cite the utility in surface overcoatings (Park et al., Biomaterials 1998, 19, 851).
Utility of germinants in solution have also been previously reported to aid in the conversion of spores into the vegetative cellular form; however, no mention of using this in decontamination was made (Cross et al.).
Bacteriocides have received much attention by way of industrial products, patent literature, as well as, peer-reviewed literature (Block, S. S. (ed.), 1991, Disinfection, sterilization and preservation, 4th edition. Lea & Febiger, Philadelphia, Pa.; Russell, A., D., W. B. Hugo and G. A. J. Ayliffe, 1992, Principles and practice of disinfection, preservation and sterilization. Blackwell Scientific Publications, London, U.K.). There have been many reports and patents dealing with the benefits of having surfaces capable of killing bacteria on contact (Ackart et al., J. Biomed. Mater. 1975, 9, 55-68; Endo et al., Appl. Environ. Microbiol. 1987, 53, 2050-2055; Gottenbos et al., Biomaterials 2002, 23, 1417-1423; Ottersbach et al., U.S. Pat. No. 5,967,714; Speir et al., J. Colloid Interface Sci. 1982, 89, 68-76; Tiller et al., Biotechnol. Bioeng. 2002, 79, 465-471; Tiller et al., Proc. Natl. Acad. Sci. 2002 98, 5981-5985; Bauth et al., U.S. Pat. No. 6,656,919). Despite the numerous reports, very few successful attempts to kill spores, more importantly the anthrax spore (Bacillus anthracis), have been made. A unique spray approach is reported; however, it requires treatment of a contaminated surface rather than serving as a preexisting coating (Bauth et al.). A common spore characteristic is the impervious outer coat. These outer coatings are very resistant to cold, heat, drought, harsh chemicals, mild radiation, many sporicides, and UV radiation (Mock et al., Annu. Rev. Microbiol. 2001, 55, 647-671).
The cell wall of a typical 1-2 μm vegetative bacterium is very complex, with multiple layers outside the cytoplasmic membrane. The structure of the cell wall consists of an outer glycocalyx capsule layer atop of an S-layer, peptidoglycan layer, and finally a plasmic membrane protecting the nucleus. In order to be effective, any biocide must be able to penetrate through this 40 nm outer wall consisting of layers such as glycocalyx, S-layer, peptidoglycan lipoteichoic acid layers to reach the vital parts in order to have an effect. Bactericidal functional groups are well known and are documented to target the cell membrane. Such products are currently commercially available as antiseptics, disinfectants, preservatives, sanitizers, water treatments, and swimming pool treatments. It has been reported that the bactericide mechanism starts with the adsorption onto a bacterial cell carboxylate surface followed by diffusion through the outer layers of the cell. The bonding to the cytoplasmic membrane and disruption of this membrane to result in the release of K+ ions through leakage occurs, which results in degradation of the cell structure and release of cell contents, thus resulting in the death of the cell.
Quaternary ammonium, pyridinium, and phenolic compounds are known to possess biocidal activity and have been used in a variety of applications and numerous commercially available products. These compounds have not only found utility as biocides but also as phase transfer catalysts and mobility systems designed to aid in the drug delivery processes. They have also been reported to possess antiseptic properties.